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We measured dissolved isoprene (2-methyl-1,3-butadiene; CH) concentrations in a broad area of the southern Indian Ocean and in the Indian sector of the Southern Ocean from 35°S to 64°S and from 37°E to 111°E during austral summer 2010-2011. Isoprene concentrations were continuously measured by use of a proton-transfer-reaction mass spectrometer combined with a bubbling-type equilibrator. Concentrations of isoprene and its emission flux throughout the study period ranged from 0.2 to 395 pmol L and from 181 to 313 nmol m day, respectively, the averages being generally higher than those of previous studies. Although we found a significant linear positive relationship between isoprene and chlorophyll- a concentrations ( r = 0.37, n = 36, P < 0.001), the correlation coefficient was lower than previously reported. In contrast, in the high-latitude area (>53°S) we identified a significant negative correlation ( r = 0.59, n = 1263, P < 0.001) between isoprene and the temperature-normalized partial pressure of carbon dioxide (n-pCO), used as an indicator of net community production in this study. This suggests that residence times and factors controlling variations in isoprene and n-pCO are similar within a physically stable water column. [ABSTRACT FROM AUTHOR]

In order to clarify the CO2 exchange between the seawater and the overlying air during the sea-ice formation, we have carried out tank experiments in a low-temperature room. CO2 concentration above the sea-ice began to increase since the beginning of the sea-ice formation, and increased at larger rates with time and the decrease in air temperature. This increase of CO2 concentration in air was mainly caused by the increase in dissolved inorganic carbon concentration in the brine of the upper part of sea-ice, changes in CO2 solubility and dissociation constants of carbonic acid. The CO2 flux increased logarithmically with time, and reached a level of 2 × 10−4 to 5 × 10−4 g-C m−2 hr−1 at 50 mm ice thickness. We found that the CO2 flux was correlated well with the salinity and negatively with the volume of the brine in the upper part of the sea-ice. These suggested the larger role of the difference in partial pressure of CO2 between brine and air as compared to that of competitive change in the brine volume. Present results suggest the necessity to examine the CO2 exchange between the seawater and air in seasonal sea-ice areas. [ABSTRACT FROM AUTHOR]

Measurements of the partial pressure of CO2 in surface seawaterwere made in the Southern Ocean south of Australia during four cruises in January to February 1969, December 1983 to January 1984, December 1994 to January 1995 and January 2002. The spatial distribution offor the four cruises showed the same pattern north of the Sub-Antarctic Front (SAF), while year-to-year changes were noted south of the SAF. We evaluated the long-term trend of therepresentative of the zone between oceanographic fronts by taking into account changes in the seasonal variation inand the long-term increase of the sea-surface temperature (SST) of the Southern Hemisphere. The observed growth rate ofwas 0.7± 0.1μatm yr−1 at its minimum, which was observed at the SST of 15°C north of the Subtropical Front (STF), 1.0± 0.5μatm yr−1 in the Sub-Antarctic Zone (SAZ) between STF and SAF, 1.5± 0.4μatm yr−1 in the Polar Frontal Zone (PFZ) between SAF and the Polar Front (PF) and 1.8± 0.2μatm yr−1 in the Polar Zone (PZ) between PF and 62°S, determined as the northern edge of the Seasonal Sea Ice Zone (SSIZ) on the basis of surface salinity and satellite images. These increases were caused by the uptake of anthropogenic CO2 as well as variations in the thermodynamic temperature effect, ocean transport and biological activity. In the SSIZ between 62 and 66.5°S, we could not clearly evaluate the long-term trend ofdue to the remarkable CO2 drawdown due to biological activity in January 2002. The relatively low growth rates ofclose to the STF and in the SAZ are probably associated with the formation of Subtropical Mode Water and Sub-Antarctic Mode Water in their respective zones. Between the north of the STF and the PZ, the growth rate of total dissolved inorganic carbon was calculated to be about 0.5–0.8μmol kg−1 yr−1 via the buffer factor. [ABSTRACT FROM AUTHOR]